/Engine/Source/Runtime/GeometryCore/Public/Selections/MeshConnectedComponents.h
Find all connected triangle components of a subset of triangles of the Mesh and store in Components array. Triangle connectivity is based on edge connectivity, ie bowtie-vertices are not connections between triangles.
void FindConnectedTriangles ( const [TArray](API\Runtime\Core\Containers\TArray)< int > & TriangleROI, [TFunction](API\Runtime\Core\GenericPlatform\TFunction)< bool(int32, int32)> TrisConnectedPredicate )